Question

How do you know that the pea wrinkle-seed allele is a recessive allele?

Answer 1

I hope this is correct:

The allele for wrinkled seed shape in garden peas is considered recessive because the trait associated with the allele is not expressed in heterozygotes. Heterozygotes are individuals that have two different alleles for a particular gene locus.

SHORT ANSWER: The trait associated with the allele is not exhibited in heterozygotes.